MYB transcription factors (TFs) are one of the largest TF families in plants to regulate numerous biological processes. However, our knowledge of the MYB family in Physcomitrella patens is limited. We identified 116 MYB genes in the P. patens genome, which were classified into the R2R3-MYB, R1R2R3-MYB, 4R-MYB, and MYB-related subfamilies. Most R2R3 genes contain 3 exons and 2 introns, whereas R1R2R3 MYB genes contain 10 exons and 9 introns. N3R-MYB (novel 3RMYB) and NR-MYBs (novel RMYBs) with complicated gene structures appear to be novel MYB proteins. In addition, we found that the diversity of the MYB domain was mainly contributed by domain shuffling and gene duplication. RNA-seq analysis suggested that MYBs exhibited differential expression to heat and might play important roles in heat stress responses, whereas CCA1-like MYB genes might confer greater flexibility to the circadian clock. Some R2R3-MYB and CCA1-like MYB genes are preferentially expressed in the archegonium and during the transition from the chloronema to caulonema stage, suggesting their roles in development. Compared with that of algae, the numbers of MYBs have significantly increased, thus our study lays the foundation for further exploring the potential roles of MYBs in the transition from aquatic to terrestrial environments.

The development and tissue-dependent color formation of the horticultural plant results in various color pattern flowers. Anthocyanins and carotenoids contribute to the red and yellow colors, respectively. In this study, quantitative real-time polymerase chain reaction (qRT-PCR) is used to analyze the expression profiles of anthocyanin and carotenoids biosynthesis genes in Cymbidium lowianum (Rchb.f.) Rchb.f. Appropriate reference gene selection and validation are required before normalization of gene expression in qRT-PCR analysis. Thus, we firstly selected 12 candidate reference genes from transcriptome data, and used geNorm and Normfinder to evaluate their expression stability in lip (divided into abaxial and adaxial), petal, and sepal of the bud and flower of C. lowianum. Our results show that the two most stable reference genes in different tissues of C. lowianum bud and flower are EF1δ and 60S, the most unstable reference gene is 26S. The expression profiles of the CHS and BCH genes were similar to FPKM value profiles after normalization to the two most stable reference genes, EF1δ and 60S, with the upregulated CHS and BCH expression in flower stage, indicating that the ABP and CBP were activated across the stages of flower development. However, when the most unstable reference gene, 26S, was used to normalize the qRT-PCR data, the expression profiles of CHS and BCH differed from FPKM value profiles, indicating the necessity of selecting stable reference genes. Moreover, CHS and BCH expression was highest in the abaxial lip and adaxial lip, respectively, indicating that the ABP and CBP were activated in abaxial and adaxial lip, respectively, resulting in a presence of red or yellow segments in abaxial and adaxial lip. This study is the first to provide reference genes in C. lowianum, and also provide useful information for studies that aim to understand the molecular mechanisms of flower color formation in C. lowianum.

As globally important ornamental and medicinal plants, orchids exhibit significant differences in the difficulty and pathways of in vitro regeneration. Most orchid species can directly form protocorm-like bodies (PLBs) through the differentiation of shoot tips or other explants, which then regenerate into new plantlets, while some species form callus through explant dedifferentiation followed by PLB differentiation from the callus. At present, the regenerative mechanisms underlying PLB and callus in orchids, as well as the key factors influencing their differentiation, remain poorly elucidated. In this study, seedlings of Dendrobium officinale obtained from aseptic seed germination were used to investigate the effects of explant type, 2,4-D concentration, temperature, light intensity and photoperiod on the induction of PLBs and callus. The results showed that there were no significant differences in callus induction among the tested explants in D. officinale, whereas stem nodal segments were more suitable for PLB induction. For both internodal and nodal segments, the incidence rate of callus formation was higher than that of PLBs. The concentration of 2,4-D influenced the induction direction of the explants; higher concentration promoted PLB induction, while lower concentration was sufficient for callus formation. Low temperature and low light intensity inhibited PLB induction while promoting callus formation in D. officinale. High temperature and intense light partially caused desiccation of explants. A temperature of 25/22 °C (day/night) and a photosynthetic photon flux density of 50 µmol m⁻² s⁻¹ were more suitable for callus or PLB induction in D. officinale. A shorter photoperiod favored callus induction, while a longer photoperiod was beneficial for PLB induction. This study reveals the differences in influencing factors for PLB and callus induction in D. officinale, providing important insights for the propagation of orchid seedlings and laying a significant foundation for elucidating the mechanisms of PLB and callus induction.

Pleione bulbocodioides, a world-renowned ornamental orchid, exhibits a pronounced winter dormancy in its floral buds, thereby presenting a spring flowering